The breaking capacity, also known as the short-circuit capacity, refers to the maximum current that the fuse can reliably break under the rated voltage. Under fault or short-circuit conditions, the fuse will be subjected to instantaneous overload several times or even dozens of times the rated current. Safe operation requires the fuse to remain intact (without explosion or body rupture) and to clear the fault. The expected fault current of the circuit where the fuse is placed must be less than the rated breaking current specified by the standard, otherwise, when the fault causes the fuse to blow, there will be continuous arcing, ignition, fuse burning, melting together with the contacts, and fuse markings that cannot be identified, etc.
Multiply the number of sets of electrical windings or other components by the voltage each offers. For example, if you are calculating the breaking capacity connected with a three-phase 520-volt transformer, multiply 3 by 520, giving 1,560 volts.
Divide the volt-amperage running through the circuit by this voltage. For example, if the transformer runs at 78,000 volt-amperes, divide 78,000 by 1,560, giving 50 amperes.
The rated breaking capacity (in the UL file) is directly related to the rated current and load voltage of the fuse. The greater the rated current, the greater the breaking capacity; the higher the load voltage, the lower the breaking capacity.
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